Bioguided isolation, identification and bioactivity evaluation of anti-MRSA constituents from Morus alba Linn

Anti-MRSA mechanism of spirostane saponin in Rohdea pachynema F.T.Wang & tang

ETHNOPHARMACOLOGY RELEVANCE

Rohdea pachynema F.T.Wang & Tang (R. pachynema), is a traditional folk medicine used for the treatment of stomach pain, stomach ulcers, bruises, and skin infections in China. Some of the diseases may relate to microbial infections in traditional applications. However few reports on its antimicrobial properties and bioactive components.

AIM OF THE STUDY

To identify its bioactive constituents against methicillin-resistant Staphylococcus aureus (MRSA) in vitro and in vivo, and its mechanism.

MATERIALS AND METHODS

The anti-MRSA ingredient 6α-O-[β-D-xylopyranosyl-(1 → 3)-β-D-quinovopyranosyl]-(25S)-5α-spirostan-3β-ol (XQS) was obtained from R. pachynema by phytochemical isolation. Subsequently, XQS underwent screening using the broth microdilution method and growth inhibition curves to assess its antibacterial activity. The mechanism of XQS was evaluated by multigeneration induction, biofilm resistance assay, scanning electron microscopy, transmission electron microscopy, and metabolomics. Additionally, a mouse skin infection model was established in vivo.

RESULTS

26 compounds were identified from the R. pachynema, in which anti-MRSA spirostane saponin (XQS) was reported for the first time with a minimum inhibitory concentration (MIC) of 8 μg/mL. XQS might bind to peptidoglycan (PGN) of the cell wall, phosphatidylglycerol (PG), and phosphatidylethanolamine (PE) of the cell membrane, then destroying the cell wall and the cell membrane, resulting in reduced membrane fluidity and membrane depolarization. Furthermore, XQS affected MRSA lipid metabolism, amino acid metabolism, and ABC transporters by metabolomics analysis, which targeted cell walls and membranes causing less susceptibility to drug resistance. Furthermore, XQS (8 mg/kg) recovered skin wounds in mice infected by MRSA effectively, superior to vancomycin (8 mg/kg).

CONCLUSIONS

XQS showed anti-MRSA bioactivity in vitro and in vivo, and its mechanism association with cell walls and membranes was reported for the first, which supported the traditional uses of R. pachynema and explained its sensitivity to MRSA.

Lab-on-a-chip: an advanced technology for the modernization of traditional Chinese medicine

Benefiting from the complex system composed of various constituents, medicament portions, species, and places of origin, traditional Chinese medicine (TCM) possesses numerous customizable and adaptable efficacies in clinical practice guided by its theories. However, these unique features are also present challenges in areas such as quality control, screening active ingredients, studying cell and organ pharmacology, and characterizing the compatibility between different Chinese medicines. Drawing inspiration from the holistic concept, an integrated strategy and pattern more aligned with TCM research emerges, necessitating the integration of novel technology into TCM modernization. The microfluidic chip serves as a powerful platform for integrating technologies in chemistry, biology, and biophysics. Microfluidics has given rise to innovative patterns like lab-on-a-chip and organoids-on-a-chip, effectively challenging the conventional research paradigms of TCM. This review provides a systematic summary of the nature and advanced utilization of microfluidic chips in TCM, focusing on quality control, active ingredient screening/separation, pharmaceutical analysis, and pharmacological/toxicological assays. Drawing on these remarkable references, the challenges, opportunities, and future trends of microfluidic chips in TCM are also comprehensively discussed, providing valuable insights into the development of TCM.

Plant Flavonoids with Antimicrobial Activity against Methicillin-Resistant Staphylococcus aureus (MRSA)

Methicillin-resistant Staphylococcus aureus (MRSA) has become a serious threat to human public health and global economic development, and there is an urgent need to develop new antimicrobial agents. Flavonoids are the largest group of plant secondary metabolites, and the anti-S. aureus and anti-MRSA activities of flavonoids have now been widely reported. The aim of this Review is to describe plant-derived flavonoid active ingredients and their effects and mechanisms of inhibitory activity against MRSA in order to provide insights for screening novel antimicrobial agents. Here, 85 plant-derived flavonoids (14 flavones, 21 flavonols, 26 flavanones, 9 isoflavones, 12 chalcones, and 3 other classes) with anti-MRSA activity are reviewed. Among these flavonoids, flavones and isoflavones generally showed the most significant anti-MRSA activity (MICs: 1-8 μg/mL). The results of the present Review display that most of the flavonoids with excellent anti-MRSA activity were derived from Morus alba L. and Paulownia tomentosa (Thunb.) Steud. The antibacterial mechanism of flavonoids against MRSA is mainly achieved by disruption of membrane structures, inhibition of efflux pumps, and inhibition of β-lactamases and bacterial virulence factors. We hope this Review can provide insights into the development of novel antimicrobials based on natural products for treating MRSA infections.

Structure optimizing of flavonoids against both MRSA and VRE

Methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococci (VRE) cause more than 100,000 deaths each year, which need efficient and non-resistant antibacterial agents. SAR analysis of 162 flavonoids from the plant in this paper suggested that lipophilic group at C-3 was crucial, and then 63 novel flavonoid derivatives were designed and total synthesized. Among them, the most promising K15 displayed potent bactericidal activity against clinically isolated MRSA and VRE (MICs = 0.25-1.00 μg/mL) with low toxicity and high membrane selectivity. Moreover, mechanism insights revealed that K15 avoided resistance by disrupting biofilm and targeting the membrane, while vancomycin caused 256 times resistance against MRSA, and ampicillin caused 16 times resistance against VRE by the same 20 generations inducing. K15 eliminated residual bacteria in mice skin MRSA-infected model (>99 %) and abdominal VRE-infected model (>92 %), which was superior to vancomycin and ampicillin.

Prenylated Flavonoids of the Moraceae Family: A Comprehensive Review of Their Biological Activities

Prenylated flavonoids (PFs) are natural flavonoids with a prenylated side chain attached to the flavonoid skeleton. They have great potential for biological activities such as anti-diabetic, anti-cancer, antimicrobial, antioxidant, anti-inflammatory, enzyme inhibition, and anti-Alzheimer's effects. Medicinal chemists have recently paid increasing attention to PFs, which have become vital for developing new therapeutic agents. PFs have quickly developed through isolation and semi- or full synthesis, proving their high value in medicinal chemistry research. This review comprehensively summarizes the research progress of PFs, including natural PFs from the Moraceae family and their pharmacological activities. This information provides a basis for the selective design and optimization of multifunctional PF derivatives to treat multifactorial diseases.

A dual mechanism with H2S inhibition and membrane damage of morusin from Morus alba Linn. against MDR-MRSA

It's urgent to discover new antibiotics along with the increasing emergence and dissemination of multidrug resistant (MDR) bacterial pathogens. In the present investigation, morusin exhibited rapid bactericidal activity against methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE) by targeting the phospholipid of bacterial inner membrane, increasing membrane rigidity and disrupting bacterial homeostasis together with the membrane permeability, which caused fundamental metabolic disorders. Furthermore, morusin can also accumulate ROS, suppress H2S production, and aggravate oxidative damage in bacteria. Importantly, morusin also inhibited the spread of wounds and reduced the bacterial burden in the mouse model of skin infection caused by MRSA. It's a chance to meet the challenge of existing antibiotic resistance and avoid the development of bacterial resistance, given the multiple targets of morusin.

Ormosianines A-P, Structurally Diverse Quinolizidine Alkaloids with AChE Inhibitory Effects from Ormosia yunnanensis

Sixteen new quinolizidine alkaloids (QAs), named ormosianines A-P (1-16), and 18 known congeners (17-34) were isolated from the stems and leaves of Ormosia yunnanensis. The structures were elucidated based on spectroscopic analyses and electron circular dichroism (ECD) calculations. Structurally, ormosianines A (1) and B (2) are the first examples of cytisine and Ormosia-type alkaloids with the cleavage of the piperidine ring. Results of the acetylcholinesterase (AChE) inhibitory assay revealed that the pentacycline Ormosia-type QAs, including 1, 16, 24, and 27-29, are good AChE inhibitors. Ormosianine A (1) exhibited more potent AChE inhibitory activity with an IC50 value of 1.55 μM. Molecular docking revealed that 1 might bind to the protein 1DX4, forming two hydrogen bonds with residues SER-238 and HIS-480.

Biochemometry identifies ostruthin as pluripotent antimicrobial and anthelmintic agent from masterwort

The root extract of Peucedanum ostruthium (PO-E) was identified as a promising antibacterial source from a screening of 158 extracts against Staphylococcus aureus. It has also recently been shown to significantly decrease the survival of the nematode Caenorhabditis elegans. We used the biochemometric approach ELINA to investigate the phytochemical characteristics of the multicomponent mixture PO-E to identify the anti-infective constituent(s) targeting S. aureus and C. elegans.1H NMR spectra of PO-E-derived microfractions were correlated with their respective bioactivity data. Heterocovariance analyses unambiguously identified ostruthin as an anti-staphylococcal constituent, which potently also inhibited Enterococcus spp.. ELINA demonstrated that anthelmintic activity was due to a combinatorial effect of ostruthin and isoimperatorin. A C. elegans-based survival and motility assay confirmed that isoimperatorin, imperatorin, and verapamil modulated the susceptibility of ostruthin. The combinatorial effect of these natural products was shown in larvae studies to be related to the function of the nematodes' efflux pump.

Total Synthesis of Kuwanons A and B and Discovery of Their Antibacterial Mechanism

Kuwanons A (1) and B (2) are two natural prenylated flavones isolated from the root bark of Morus alba L. In this study, the first total syntheses of kuwanons A (1) and B (2) were achieved from a common intermediate with overall yields of 6.6% and 11.6%, respectively. Kuwanon B (2) exhibited antibacterial activity against Gram-positive bacteria and concentration-dependent bactericidal activity against Staphylococcus aureus bacteria. Preliminary mechanism of action studies suggested that this compound killed bacteria rapidly by disrupting bacterial membrane integrity.

Prenylated phenolics from Morus alba against MRSA infections as a strategy for wound healing

Antimicrobial resistance is a public health threat and the increasing number of multidrug-resistant bacteria is a major concern worldwide. Common antibiotics are becoming ineffective for skin infections and wounds, making the search for new therapeutic options increasingly urgent. The present study aimed to investigate the antibacterial potential of prenylated phenolics in wound healing. Phenolic compounds isolated from the root bark of Morus alba L. were investigated for their antistaphylococcal potential both alone and in combination with commonly used antibiotics. The minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) were determined by microdilution and agar method. Synergy was investigated using the checkerboard titration technique. Membrane-disrupting activity and efflux pump inhibition were evaluated to describe the potentiating effect. Prenylated phenolics inhibited bacterial growth of methicillin-resistant Staphylococcus aureus (MRSA) at lower concentrations (MIC 2-8 μg/ml) than commonly used antibiotics. The combination of active phenolics with kanamycin, oxacillin, and ciprofloxacin resulted in a decrease in the MIC of the antimicrobial agent. Kuwanon C, E, T, morusin, and albafuran C showed synergy (FICi 0.375-0.5) with oxacillin and/or kanamycin. Prenylated phenolics disrupted membrane permeability statistically significantly (from 28 ± 16.48% up to 73 ± 2.83%), and membrane disruption contributes to the complex antibacterial activity against MRSA. In addition, kuwanon C could be considered an efflux pump inhibitor. Despite the antibacterial effect on MRSA and the multiple biological activities, the prenylated phenolics at microbially significant concentrations have a minor effect on human keratinocyte (HaCaT) viability. In conclusion, prenylated phenolics in combination with commonly used antibiotics are promising candidates for the treatment of MRSA infections and wound healing, although further studies are needed.

Mulberry Diels-Alder-type adducts: isolation, structure, bioactivity, and synthesis

Mulberry Diels-Alder-type adducts (MDAAs) are unique phenolic natural products biosynthetically derived from the intermolecular [4 + 2]-cycloaddition of dienophiles (mainly chalcones) and dehydroprenylphenol dienes, which are exclusively distributed in moraceous plants. A total of 166 MDAAs with diverse skeletons have been isolated and identified since 1980. Structurally, the classic MDAAs characterized by the chalcone-skeleton dienophiles can be divided into eight groups (Types A - H), while others with non-chalcone dienophiles or some variations of classic MDAAs are non-classic MDAAs (Type I). These compounds have attracted significant attention of natural products and synthetic chemists due to their complex architectures, remarkable biological activities, and synthetic challenges. The present review provides a comprehensive summary of the structural properties, bioactivities, and syntheses of MDAAs. Cited references were collected between 1980 and 2021 from the SciFinder, Web of Science, and China National Knowledge Internet (CNKI).

LC-MS Metabolite Profiling and the Hypoglycemic Activity of Morus alba L. Extracts

Morus alba L. is used in traditional Chinese medicine for its anti-diabetic activity; however, the part of the hypoglycemic activity and related active metabolites are still not fully clarified. In this study, the metabolites in the M. alba roots, leaves, twigs, and fruits extracts (70% ethanol extracts) were systematically identified, and their hypoglycemic activity was evaluated by the high-fat diet/streptozotocin-induced 2 diabetes mellitus (T2D) mouse model. A total of 60 high-level compounds, including 16 polyphenols, 43 flavonoids, and one quinic acid, were identified by high-performance liquid chromatography/quadrupole time-of-flight mass spectrometry (HPLC-Q-TOF-MS) combined with the fragmentation pathways of standards and the self-established database. Among them, 23 metabolites were reported for the first time from this plant. In contrast to the extracts of M. alba leaves and fruits, the extracts of roots and twigs displayed significant hypoglycemic activity The glycemia was significantly reduced from 32.08 ± 1.27 to 20.88 ± 1.82 mmol/L and from 33.32 ± 1.98 to 24.74 ± 1.02 mmol/L, respectively, after 4 weeks of treatment with roots and twigs extracts. Compound 46 (morusin), which is a high-level component identified from the extracts of M. alba roots, also displayed significant activity in decreasing the blood glucose level of T2D mice reduced from 31.45 ± 1.23 to 23.45 ± 2.13 mmol/L. In addition, the extracts of roots and twigs displayed significant activity in reducing postprandial glycemia. This work marks the first comparison of the metabolites and hypoglycemic activity of M. alba roots, leaves, twigs, and fruits extracts, and provides a foundation for further development of M. alba extracts as anti-diabetic drugs.

Prenylated Flavonoids in Topical Infections and Wound Healing

The review presents prenylated flavonoids as potential therapeutic agents for the treatment of topical skin infections and wounds, as they can restore the balance in the wound microenvironment. A thorough two-stage search of scientific papers published between 2000 and 2022 was conducted, with independent assessment of results by two reviewers. The main criteria were an MIC (minimum inhibitory concentration) of up to 32 µg/mL, a microdilution/macrodilution broth method according to CLSI (Clinical and Laboratory Standards Institute) or EUCAST (European Committee on Antimicrobial Susceptibility Testing), pathogens responsible for skin infections, and additional antioxidant, anti-inflammatory, and low cytotoxic effects. A total of 127 structurally diverse flavonoids showed promising antimicrobial activity against pathogens affecting wound healing, predominantly Staphylococcus aureus strains, but only artocarpin, diplacone, isobavachalcone, licochalcone A, sophoraflavanone G, and xanthohumol showed multiple activity, including antimicrobial, antioxidant, and anti-inflammatory along with low cytotoxicity important for wound healing. Although prenylated flavonoids appear to be promising in wound therapy of humans, and also animals, their activity was measured only in vitro and in vivo. Future studies are, therefore, needed to establish rational dosing according to MIC and MBC (minimum bactericidal concentration) values, test potential toxicity to human cells, measure healing kinetics, and consider formulation in smart drug release systems and/or delivery technologies to increase their bioavailability.

Phytochemical and anti-MRSA constituents of Zanthoxylum nitidum

Infectious diseases caused by multidrug-resistant bacteria such as methicillin-resistant Staphylococcus aureus, pose a significant threat to humanity. Persistent and repeated invasive infection with MRSA led to higher morbidity and mortality, and required comprehensive measures in treatment and prevention. Zanthoxylum nitidum (Roxb.) DC. is used as detoxifying, analgesic, and hemostatic herbal medicine for thousands of years. Previously pharmacological studies showed that Z. nitidum had antibacterial bioactivity, but only the MIC of a few compounds, crude extracts, and fractions were reported. In our ongoing endeavor to explore bioactive compounds, two new coumarins, 6-(3-oxo-butyl)-limettin (1) and toddalin I (2), and 24 known compounds were isolated from the roots of Z. nitidum, in which two isoquinoline alkaloids, 6-acetonyl-dihydrofagaridine (16) and 6-acetonyl-dihydrochelerythrine (17) showed anti-MRSA bioactivity in vitro and in vivo. Both 16 and 17 showed synergistic action with ampicillin, which decreased the MIC significantly, and both compounds had a significant ability to destroy bacterial biofilm combined with ampicillin. The combined administration showed a strong scavenging effect on the planktonic bacteria in vitro and cleared skin infection effectively in the model of wound infection in vivo. Furthermore, compound 16 inhibited the efflux of the drug by combining with ampicillin or EtBr, resulting in the MIC decreased obviously. Our investigation supported the traditional use of Z. nitidum in treating infections caused by bacteria, and might provide new natural products to reduce the use of antibiotics and the treatment of drug-resistance bacteria.